(physics) A characteristic of the transition of a system or process from regular motion to chaos, in which the period of one of its parameters is seen to double.

The 45-year reign of Emperor Meiji (1868-1912). During this time, Japan started its modernization and rose to world power status.

(mathematics) Any function whose value repeats after the regular addition of a period to its independent variable; i.e., a function ƒ such that, for some positive constant p, ƒ(x + p) = ƒ(x) for all x.

(idiomatic) A length of time during which rules or penalties are waived or deferred.

a school period in which a student has free time, i.e., is not enrolled in a class.

(astronomy) Taking over 200 years to complete an orbit; especially said of comets.

Any of certain species of cicadas, especially in genus Magicicada, which are known for their 17- and 13-year life-cycles, during most of which they develop underground, emerging in large numbers for a short time as large and audible adults, all those emerging in a year constituting a brood.

(physics) Half of the period of a wave etc; typically the time taken for part of a wave to be replaced by a similar part that is out of phase.

plural of periodic table

(of an astronomic object) The time taken to rotate about its axis relative to the background stars.